#include <stdio.h>

int main(int argc, const char *argv[])
{
	int score = 0;
	printf("请输入一个成绩:");
	scanf("%d", &score);

	if(score < 0 || score > 100){
		printf("请输入合法的成绩[0,100]\n");
		return -1;
	}

	if(90 <= score && score <= 100){
		printf("A\n");
	}else if(score >= 80 && score < 90){
		printf("B\n");
	}else if(score >= 70 && score < 80){
		printf("C\n");
	}else if(score >= 60 && score < 70){
		printf("D\n");
	}else{
		printf("不及格\n");
	}

	return 0;
}
